Polycyclic aromatic hydrocarbons (PAH) are major contaminants in soil and groundwater at a number of sites across the United States. Many of them are known or suspected carcinogens, yet many are also known to be biodegradable by bacteria and fungi indigenous to native and contaminated soils. Biological processes have been used to remediate PAH contaminated soils, but removal of the high molecular weight (HMW), carcinogenic species is often incomplete. Far less is known about the biodegradation of HMW PAH (defined as those with four or more rings) than is known about the degradation of two- and three ring compounds. Some bacteria recently have been found to grow on four-ring PAH, while others only cometabolize these compounds. The purposes of this project are to study the metabolism and biodegradation of HMW PAH, with particular emphasis on identifying products of incomplete metabolism that may accumulate in the aqueous phase; to study the kinetics of HMW PAH degradation; to asses the influence of other PAH on the rate of HMW PAH degradation when present in mixtures; to evaluate potential inducers of HMW PAH metabolism which might be used to sustain the growth of bacteria that cometabolize HMW PAH after their principal growth substrates are depleted; to evaluate the influence of mass transfer processes on the rate and extent of HMW PAH degradation; and to evaluate strategies to increase the extent of HMW PAH degradation in mass transfer-limited situations. These aims will be met using PAH degrading bacteria already isolated from a variety of contaminated soils and which appear to contain different pathways for PAH metabolism/ some of these bacteria also have characteristics which may allow them to influence mass transfer processes. These bacteria will be screened for evidence of metabolite production using spectroscopic methods and mass balances with radiolabeled substrates. Analysis of metabolites will employ evolving techniques in mass spectrometry to aid in the identification of polar, non-volatile compounds. Mass transfer processes of interest include dissolution of PAH from non- aqueous phases and desorption from soil organic matter. Quantitative models will be developed to ascertain that biodegradation can be quantified using independently measured rate parameters, and as a tool in identifying those organisms that may influence mass transfer processes. Strategies to improve the biodegradability of HMW PAH will pounds as growth substrates and the use of nonionic surfactants to increase the bioavailability of these compounds.